•Request—Sent to the multicast address 224.0.0.9 to request route updates from other RIP-enabled routers.

•Response—Sent every 30 seconds by default (see the "Verifying the RIP Configuration" section). The router also sends response messages after it receives a Request message. The response message contains the entire RIP route table. RIP sends multiple response packets for a request if the RIP routing table cannot fit in one response packet.

RIP uses a hop countfor the routing metric. The hop count is the number of routers that a packet can traverse before reaching its destination. A directly connected network has a metric of 1; an unreachable network has a metric of 16. This small range of metrics makes RIP an unsuitable routing protocol for large networks.

RIPv2 Authentication

You can configure authentication on RIP messages to prevent unauthorized or invalid routing updates in your network. Cisco NX-OS supports a simple password or an MD5 authentication digest.

You can configure the RIP authentication per interface by using key-chain management for the authentication keys. Key-chain management allows you to control changes to the authentication keys used by an MD5 authentication digest or simple text password authentication. See theCisco Nexus 7000 Series NX-OS Security Configuration Guide, Release 5.x, for more details about creating key-chains.

To use an MD5 authentication digest, you configure a password that is shared at the local router and all remote RIP neighbors. Cisco NX-OS creates an MD5 one-way message digest based on the message itself and the encrypted password and sends this digest with the RIP message (Request or Response). The receiving RIP neighbor validates the digest by using the same encrypted password. If the message has not changed, the calculation is identical and the RIP message is considered valid.

An MD5 authentication digest also includes a sequence number with each RIP message to ensure that no message is replayed in the network.

Split Horizon

You can use split horizon to ensure that RIP never advertises a route out of the interface where it was learned.

Split horizon is a method that controls the sending of RIP update and query packets. When you enable split horizon on an interface, Cisco NX-OS does not send update packets for destinations that were learned from this interface. Controlling update packets in this manner reduces the possibility of routing loops.

You can use split horizon with poison revers to configure an interface to advertise routes learned by RIP as unreachable over the interface that learned the routes. Figure 10-1 shows a sample RIP network with split horizon with poison reverse enabled.

Route Filtering

You can configure a route policy on a RIP-enabled interface to filter the RIP updates. Cisco NX-OS updates the route table with only those routes that the route policy allows.

Route Summarization

You can configure multiple summary aggregate addresses for a specified interface. Route summarization simplifies route tables by replacing a number of more-specific addresses with an address that represents all the specific addresses. For example, you can replace 10.1.1.0/24, 10.1.2.0/24, and 10.1.3.0/24 with one summary address, 10.1.0.0/16.

If more specific routes are in the routing table, RIP advertises the summary address from the interface with a metric equal to the maximum metric of the more specific routes.

Note Cisco NX-OS does not support automatic route summarization.

Route Redistribution

You can use RIP to redistribute static routes or routes from other protocols. When you configure redistribution use a route policy to control which routes are passed into RIP. A route policy allows you to filter routes based on attributes such as the destination, origination protocol, route type, route tag, and so on. For more information, see Chapter 14 "Configuring Route Policy Manager."

Whenever you redistribute routes into a RIP routing domain, by default Cisco NX-OS does not redistribute the default route into the RIP routing domain. You can generate a default route into RIP, which can be controlled by a route policy.

You also configure the default metric that is used for all imported routes into RIP.

Load Balancing

You can use load balancing to allow a router to distribute traffic over all the router network ports that are the same distance from the destination address. Load balancing increases the utilization of network segments and increases effective network bandwidth.

Cisco NX-OS supports the Equal Cost Multiple Paths (ECMP) feature with up to 16 equal-cost paths in the RIP route table and the unicast RIB. You can configure RIP to load balance traffic across some or all of those paths.

You can configure up to four RIP instances on a VDC. By default, Cisco NX-OS places you in the default VDC and default VRF unless you specifically configure another VDC and VRF. See the Cisco NX-OS Virtual Device Context Configuration Guide and Chapter 12 "Configuring Layer 3 Virtualization."

Licensing Requirements for RIP

The following table shows the licensing requirements for this feature:

Product

License Requirement

Cisco NX-OS

RIP requires no license. Any feature not included in a license package is bundled with the Cisco NX-OS system images and is provided at no extra charge to you. For a complete explanation of the Cisco NX-OS licensing scheme, see the Cisco NX-OS Licensing Guide.

Note Make sure the LAN Base Services license is installed on the switch to enable Layer 3 interfaces.

Configuring Route Summarization

You can create aggregate addresses that are represented in the routing table by a summary address. Cisco NX-OS advertises the summary address metric that is the smallest metric of all the more-specific routes.

To configure a summary address on an interface, use the following command in interface configuration mode:

Command

Purpose

iprip summary-address ip-prefix/mask-len

Example:

switch(config-if)# ip router rip summary-address 192.0.2.0/24

Configures a summary address for RIP for IPv4 addresses.

Configuring Route Redistribution

You can configure RIP to accept routing information from another routing protocol and redistribute that information through the RIP network. Redistributed routes can optionally be assigned a default route.

This example shows how to create a VRF and add an interface to the VRF:

switch# configure terminal

switch(config)# vrf context RemoteOfficeVRF

switch(config-vrf)# exit

switch(config)# router rip Enterprise

switch(config-router)# vrf RemoteOfficeVRF

switch(config-router-vrf)# address-family ipv4 unicast

switch(config-router-vrf-af)# redistribute eigrp 201 route-map RIPmap

switch(config-router-vrf-af)# interface ethernet 1/2

switch(config-if)# no switchport

switch(config-if)# vrf member RemoteOfficeVRF

switch(config-if)# ip address 192.0.2.1/16

switch(config-if)# ip router rip Enterprise

switch(config-if)# copy running-config startup-config

Tuning RIP

You can tune RIP to match your network requirements. RIP uses several timers that determine the frequency of routing updates, the length of time before a route becomes invalid, and other parameters. You can adjust these timers to tune routing protocol performance to better suit your internetwork needs.

Note You must configure the same values for the RIP timers on all RIP-enabled routers in your network.

You can use the following optional commands in address-family configuration mode to tune RIP:

Command

Purpose

timersbasic update timeout holddown garbage-collection

Example:

switch(config-router-af)# timers basic 40 120 120 100

Sets the RIP timers in seconds. The parameters are as follows:

•update—The range is from 5 to any positive integer. The default is 30.

•timeout—The time that Cisco NX-OS waits before declaring a route as invalid. If Cisco NX-OS does not receive route update information for this route before the timeout interval ends, Cisco NX-OS declares the route as invalid. The range is from 1 to any positive integer. The default is 180.

•holddown—The time during which Cisco NX-OS ignores better route information for an invalid route. The range is from 0 to any positive integer. The default is 180.

•garbage-collection—The time from when Cisco NX-OS marks a route as invalid until Cisco NX-OS removes the route from the routing table. The range is from 1 to any positive integer. The default is 120.

You can use the following optional commands in interface configuration mode to tune RIP:

Command

Purpose

iprip metric-offset value

Example:

switch(config-if)# ip rip metric-offset 10

Adds a value to the metric for every router received on this interface. The range is from 1 to 15. The default is 1.

Configuration Examples for RIP

This example creates the Enterprise RIP instance in a VRF and adds Ethernet interface 1/2 to this RIP instance. The example also configures authentication for Ethernet interface 1/2 and redistributes EIGRP into this RIP domain.